Metering device, component description

B14.40-0062-11

Arrangement

14 Metering unit

The metering unit (14) is located close to the last cylinder of the engine cylinder head.

Task

In the metering unit (14), compressed air and AdBlue are mixed forming an aerosol. The latter is injected in the exhaust pipe following engine control module (MR) command.

Composition

The metering unit consists of an aluminum housing, divided in two parts. On one side are the AdBlue components and on the other side the compressed air components. In the middle is the metering valve (5).

B14.40-0169-09

1 AdBlue inlet

2 AdBlue pressure sensor (17B05)

3 AdBlue temperature sensor (17B07)

4 Calibration screw

5 Metering valve (17Y03)

6 Diffuser

7 Compressed air pressure sensor (17B06)

8 Compressed air inlet

9 Aerosol outlet

10 Check valve

11.1 AdBlue screen filter

11.2 Compressed air screen filter

12 Bushing

13 Heating element (17R05)

Function

The AdBlue pump supplies the metering unit, where the AdBlue flows by the inlet (1), passing through the screen filter (11.1), with a 30 µm mesh for impurities elimination, and continues under pressure to the metering valve (5), normally closed. When starting the engine, begins the flow of compressed air through the inlet (8) that passes through he screen filter (11.2).

When the metering valve (5) opens, in intervals calculated by the engine module (MR), the AdBlue passes by it and, based on the conditions of flow and pressure, is pushed to the injection nozzle.

Due to the continuous flow of compressed air, the metering unit guarantees that there is no AdBlue residue in its inside.

Ventilation of the metering unit with the ignition turned-off

After ignition turn-off, the metering unit goes through a process of ventilation in order to avoid damage from AdBlue freezing. This operation of the control module occurs by the opening and closing of the compressed air limitation solenoid valve and of the metering valve (5) at coordinate intervals of, at maximum, 300 seconds. The main magnitudes that influence the duration of the process are the pressures in the sensors (7) and (2).

If the pressure difference remains above the specified, the valve (5) is opened, and the compressed air flows in the opposite direction to that of the AdBlue in the metering unit and pushes the rest of AdBlue to the pump module, through the piping.

When the engine module (MR) recognizes, based on the sensor signals, that the metering unit was sufficiently filled with air, the ventilation is finished. This occurs when the pressure in the sensor (7) is higher than the pressure in the sensor (2).

The piping between the pump module and the metering unit comprises a flexible hose that permits to have additional residue which are produced with the freezing of AdBlue. Besides this, the pressure in this piping is reduced to the atmospheric pressure by the pressure relief in the pump module.

Description of the heating element

In case there is crystallization in the inlet or in the throat of the diffuser (6) and the air pressure sensor (7) does not make the reading, the system will understand that there is clogging and will start a cleaning routine as follows:

1 The heating element (13) will switch-on for 640 seconds;

2 The engine module (MR) checks if there is air pressure in the sensor (7);

3 If there is pressure, the system will be ready to inject;

4 If there is no pressure the heating element (13) is switched-on again;

5 The heating element (13) only starts operating if there is need and persisting the clogging it will remain switched-on for up to 3600 seconds. If the system still remains clogged, the metering is interrupted and the fault is recorded.

The compressed air pressure in the sensor (7) of the metering unit needs to be at least at 1.5 bar to be released for injection of AdBlue.

With the vehicle operating the compressed air passes constantly by the metering unit, even if it is not injecting AdBlue.